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Beetle juice!

Sequencing the genes in an insect invader’s gut may yield answers for bioenergy and clues to the biology of invasiveness.

David Pacchioli

September 10, 2007

Beetle juice!

What's the unlikeliest place you can think of to look for alternative energy answers? How about inside the gut of an insect pest?

An invasive species native to China, the Asian long-horned beetle can eat its way through an impressive variety of hardwood trees, including maple, poplar, willow, and elm. In the U.S., where it arrived on packing crates in 1996, the pest is so far confined to New York and Chicago, and its favorite foodstuff is maple.

Penn State entomologist Kelli Hoover began studies on the beetle back in 2001. Soon she noticed something unusual. "Most cerambycids [the long-horned beetle family] attack stressed or dying trees," she explains. "This insect can attack a wide range of trees that are healthy. I got very curious about how it manages to do that."

Examining the beetle's digestive tract, she and graduate student Scott Geib found quite a variety of bacteria and a few fungi. With the help of biochemist colleague Ming Tien, they were able to characterize some of these microbes as producing enzymes that break down wood. "Scott also showed
that the larva as it is tunneling through the wood does indeed break down lignin," Hoover says.

To get a better handle on the microbial community they had found, Hoover sought out tree genomics expert John Carlson, and Maria Jimenez-Gasco, a plant pathologist who specializes in Fusarium, one of the resident fungi. Carlson was able to use ultra-high throughput genome sequencing to quickly assess the genetic makeup of the gut community.

"I wanted to know how these microbes contribute to this beetle being able to have such a broad host range," Hoover says. "How does the gut community change—our data suggest it does change—when they feed in different host trees? It's like the microbes are driving the system."

For Tien and Carlson, this was an opportunity for "bioprospecting." By metagenomic analysis—isolating DNA from the beetle gut and sequencing all the genes they find there—they hope to discover a new microbe that might be useful for bioenergy. "Maybe a previously unknown enzyme that might prove useful in removing lignin," Tien speculates. "Or we may come up with a faster cellulase, or a strategy for dealing with the crystallinity of cellulose. Basically we're asking, how does nature do it?"

Until recently, he notes, such a blanket approach would have been unthinkable, but "sequencing technology has advanced to the degree where it's possible now to get fairly good coverage of all the DNA you isolate."

"If we can discover the genes present that are responsible for extracting cellulose and degrading lignin," Carlson says, "that might have applications in treating woody biomass enzymatically for ethanol production."

Hoover's goal is more basic. "If we can understand how microbial symbionts work," she says, "I think it will tell us something about the biology of invasiveness."

Kelli Hoover, Ph.D., is associate professor of entomology in the College of Agricultural Sciences; kxh25@psu.edu. Ming Tien, Ph.D., is professor of biochemistry and molecular biology in the Eberly College of Science; mxt3@psu.edu. John E. Carlson, Ph.D., is associate professor of molecular genetics in the School of Forest Management and director of the Schatz Center for Tree Molecular Genetics; jec16@psu.edu.